This is a big gap in producing a production system based on e4. I'm dealing with this right now.
My approach is to take the org.eclipse.help.ui plugin, clone it, and add a HelpPanel control that does what HelpView does, but in a Composite. Then I can put it where I want it.
This does, unfortunately, bring in all the org.eclipse.ui stuff, but if you don't use it, it doesn't fault.
I'm working on this for the current sprint for my product. I'm aiming to get enough done that we can bring it up in our e4 UI. I've attached the HelpView.java file. THIS WILL NOT WORK AS-IS. There are missing classes other changes you have to make when you clone. I'm just providing it as a reference point.
I'm very interested in hearing other people's approaches.

Hi Jo,
We have the exact same problem at the moment and I would like to know whether it is possible to get a good help system up and going.
Did you encounter any major trouble? I have seen some posts which are connected to your work at the help system. Did you succeede or is work still in progress?

I didn't encounter any major trouble. But I rather suspect that it hasn't been fully exercised. There is probably some breakage in some of the more delicate features. However we expect it to be lightly used in our product (a deployment tool) so that's OK for us. If this was a consumer product... I'd be more nervous. As it is, we just hit feature freeze and no one has raised any red flags, so we should be shipping our e4 based product with our ported help.
Looking at the code, I think I mostly did what I suggested. I tried to do a diff, but I've got a bazillion false positives because of the date change in the (c) notice at the top.
I've attached our final HelpPanel.java below. Again, it won't work as-is, but it might help.
If that's not enough to get you going, let me know. I can either work on a better diff for what I changed, or do the paperwork necessary to publish "internal code".

Hi Jo,
I have been trying to get the help system working but for now I'm stuck at the point where the help needs the old workbench which is only available through the compatibility layer which is not an option for us to use in our program. You were talking about cloning the org.eclipse.help.ui plugin and I take it that you made some changes to it. Could you please tell me what you changed to avoid the workbench problem or maybe post the version you used?

Hey Janine.
I work for IBM and they own my brain. What that means is that anything I do is their property and I can't just always "give it away", even if I wrote it. Fortunately, IBM is fairly level headed about such things and is positive in its support of Open Source. I brought this up in a legal review we were doing and my legal rep is pretty positive that this isn't a problem. He's going to do due diligence and formally check, but he expects to be able to give me a thumbs up for not just sharing the diffs, but the complete source of the modified plugin.
Stay tuned...
Jo